The original importer should be noted on the identification tag on the driver door frame. You should have gotten a copy of the original EPA and DOT certification releases when you bought the car also, as this can be brought up when you register your car in a state with an empowered bureaucrat behind the counter and the rules are you should have them.
Like Larry said, the car had to have the odometer/speedometer changed to miles as part of the DOT certification but there is no calibration required, and often the speedometer and odometer have really poor accuracy. This can make the mileage off significantly, and can make you an inadvertent target for the cops with radar.
The clutch and transmission for a US 280E might have been a source of parts for you if they were actually imported. I do not think even the 280E was available back then with a manual transmission though, so you may have some difficulty finding replacement parts. If there was a problem with the hydraulics you would most likely see fluid leaks. Since the clutch is hydraulically operated, you should expect to have a very light feel. This is not an indication the clutch is going. Mercedes makes a shim a few mils thick that they slip into a slot on the slave cylinder that actuates the clutch. When the clutch is worn down, the rod sticking out of the slave cylinder extends further. To measure the advent of the clutch's "last legs" a slot is machined into this rod, and it aligns with the slot in the housing, allowing the shim to pass further into the housing of the slave cylinder. If you go get this tool you can keep track of the condition of the clutch relatively easily.
Hope this helps, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)